(1) Field of the Invention
The invention relates to a method of photolithographic etching of metal lines, and more particularly, to a method of photolithographic etching of metal lines without polymer residue in the manufacture of integrated circuits.
(2) Description of the Prior Art
Aluminum and aluminum alloys are often used to form metal lines in integrated circuit processing. To prevent aluminum spiking, a barrier metal layer comprising titanium, titanium nitride, titanium tungsten, or the like, is deposited underlying the aluminum layer. A second barrier metal layer also comprising titanium or titanium nitride is deposited overlying the aluminum layer as both a barrier and an anti-reflective coating layer. An oxide hard mask layer is typically formed over the metal stack. In opening the oxide hard mask, the second barrier metal layer serves as the etch stop. During this etching, a polymer will be generated which includes titanium atoms. This metallic polymer has small solubility to alkaline stripper and thus remains as residue. It is desired to remove all of the polymer to obtain a polymerless hard mask metal etching.
U.S. Pat. No. 4,915,779 to Srodes et al discloses a PE-oxide hard mask for metal etching. U.S. Pat. No. 5,665,641 to Shen et al teaches a silicon oxide or silicon nitride hard mask wherein the hard mask etching chemistry comprises CHF.sub.3 and CF.sub.4. U.S. Pat. No. 5,369,053 to Fang discloses a silicon oxynitride hard mask wherein the first etching comprises fluorine-based chemistry and etches through both the hard mask layer and the top barrier metal layer. None of these patents mentions the problem of metallic polymers.